the elements of which seem to be held together by a greenish soluble cement in which a number of minute bacteria-like rods are incorporated. The shaft of the hair—not eroded or affected in any way—can be seen intact through the encrusting fungus.
Piedra is supposed by some to be induced by the mucilaginous hair applications in vogue among the Colombians. Although Juhel-Rénoy has given to it the name "trichomycose nodulaire," it must not be confounded with the trichomycosis nodosa of Paterson (the leptothrix of Wilson), which is quite a different affection and common enough on the axillary, scrotal, and face hair in Europe and elsewhere. Neither must it be confounded with trichorexis nodosa, a
Fig. 208.—Chigger (Dermatophilus penetrans). (Blanchard.)
non-parasitic disease of the hair-shaft, which is split up at different points into brush-like bundles of fibres and is thus easily fractured; nor with moniliform hair (monilethrix, Crocker), a congenital, hereditary, and also non-parasitic disease.
Treatment.—Cleanliness, the free use of soap, and the application of some epiphyticide should suffice for cure. Should such means fail, doubtless shaving the scalp would be effectual.
4. SKIN DISEASES CAUSED BY ANIMALS
The Chigger, or Sand Flea (Dermatophilus penetrans)
This insect, formerly confined to the tropical parts of America (30° N. to 30° S.) and to the West Indies,
